Heh, that's understandable confusion - I think Fairy pokémon's weakness to Steel is to symbolise machines/technology versus myth & fantasy. Think about it, with the advent of the modern age less & less people believe in fairies. Obviously just my opinion though!
I'm not suprised at all that the Fairy type was only just classified, it happens all the time in real life. Did you guys know puffins were considered half bird, half fish for hundreds of years? The fact that science has finally caught up with Fairy types & they FINALLY get the recognition they deserve is great!
I'm happy that Gamefreak has rebalanced the types, my only issues is that I keep forgetting to consider Fairies when I'm building my team. ( T_T)